Vehicle wheel slip control system and road grade sensor therefor and method of controlling wheel slip

ABSTRACT

A vehicle wheel brake system in which vehicle and wheel speed signals are generated and utilized to generate a wheel brake pressure command signal, with a road grade sensor generating a signal reflecting the grade of the road on which the vehicle is moving. The road grade signal is used to further refine the command signal by taking into account the road grade. The system also senses brake torque and refines the command signal by considering the effect of changes in brake torque. The command signal controls mechanism, which, in turn, controls the wheel brake apply pressures.

United States Patent Edward G. Gaeke Dayton, Ohio Dec. 9, 1969 Jan. 4,1972 General Motors Corporation Detroit, Mich.

Inventor Appl. No. Filed Patented Assignee VEHICLE WHEEL SLIP CONTROLSYSTEM AND ROAD GRADE SENSOR THEREFOR AND METHOD OF CONTROLLING WHEELSLIl' 9 Claims, 10 Drawing Figs.

U.S. Cl 303/21 A, 188/ 1 81 C Int. Cl B60t 8/16 Field of Search 303/21,24,

[56] References Cited UNITED STATES PATENTS 3,131,975 5/1964 Smith et al303/21 R 3,141,707 7/1964 Nigh 303/21 A 3,235,036 2/1966 Meyer et al303/21 P Primary Examiner-Milton Buchler Assistant Examiner-John J.McLaughlin AttorneysW. E. Finken and D. D. McGraw ABSTRACT: A vehiclewheel brake system in which vehicle PATENIED JAN 41912 SHEET 2 0F 2 i wa W w w w FORCE VS SPEED VEHICLE WHEEL SPEED F,

SPEED 3Q,

T mUmOm 1 N VEN TOR. [04w 70 6: 506/4? fifl A T TORNE Y CONTROL FORCE VSROAD GRADE ROAD GRADE mumOm BRAKE TORQUE VS PER CENT SLIP a N R I! m E HT m m P E mm U H E L S W L A T YE M N L C R F E O a D N m ZOEuQmmjmUmOEMI JL D.

mDOmOP mvt mm VEHICLE WHEEL SLIP CONTROL SYSTEM AND ROAD GRADE SENSORTHEREFOR AND METHOD OF CONTROLLING WHEEL SLIP The invention relates to avehicle wheel brake control system and method and more particularly to asystem in which wheel-to-road slip is controlled and a method ofcontrolling such slip. Systems of this type are commonly referred to asantilock systems. The system in which the invention is disclosed ismechanical-hydraulic in nature, with a mechanical wheel speed sensor, amechanical vehicle speed simulator, a mechanical-hydraulic torquesensor, a mechanical-hydraulic road speed sensor, and amechanical-hydraulic wheel slip modifier.

It is a feature of the invention to utilize a signal indicating thegrade of the road on which the vehicle is moving to further refine thesignal ultimately controlling vehicle wheel braking.

The principal factors causing vehicle deceleration are the brakingefiort at the wheels, the wheel-to-road torque, and the grade of theroad on which the vehicle is moving. Systems of this type have beendevised and utilized which measure various parameters relating tobraking effort, wheel slip, and road surface conditions. It is nowproposed to further refine such systems by considering the road grade.This is an important part of the overall consideration of systemoperation when the grade varies to a significant extent. It is wellknown that vehicles being braked while ascending a large grade may bebraked more quickly, while vehicles descending a large grade may bebraked more quickly, while vehicles descending a large grade encounterthe reverse braking situation. Road grades also affect systems utilizingspeed simulators. The best signal for modifying simulated vehicle speedis to obtain a good representation of actual vehicle speed duringbraking. However, this signal is difficult to keep isolated from vehiclepitch and road grade. Developed braking effort at the wheel, or wheeltorque, provides another parameter which may be utilized to modify avehicle simulated speed signal and bring it in closer approximation withactual vehicle speed. The road grade signal is utilized to counteracterrors in vehicle speed acceleration which result when substantial roadgrades are encountered.

In the complete system embodying the invention, road grade, brake torqueand wheel speed are utilized. A simulated vehicle speed is generated andis modified by wheel brake torque and road grade. The vehicle wheelspeed signal and the vehicle simulated speed signal, as modified, arecombined and generate a wheel brake apply pressure command signal. Thissignal may also be modified by a wheel slip sensing device utilizingchanges in brake torque to affect the command signal. The command signalis presented as linear movement of a cam for controlling switches, whichin turn, control valves of a wheel brake apply pressure modulator,which, in turn, controls the application and release of wheel brakepressure.

In the drawings:

FIG. 1 is a schematic representation of a system embodying theinvention, with parts broken away and in section.

FIG. 2 is a view of the road grade sensor contained in the system ofFIG. 1, and showing the sensor in a modified position due to change inroad grade.

FIGS. 3, 4 and 5 show different positions of the switchoperating cam andthe switches under different command signal conditions.

FIG. 6 shows the general characteristics and relationship between thecommand signal and the sensed speed and the wheel speed sensor and thevehicle speed simulator, the command signal being plotted as a force.

FIG. 7 shows the general characteristics and relationship between thebrake torque signal, plotted as a force, and the torque developed by thewheel brake.

FIG. 8 shows the general characteristics and relationship between theinertia wheel speed and the sum of forces acting on the vehicle speedsimulator modifier unit.

FIG. 9 shows the general characteristics and relationship between theanticipated road grade range and the road grade output signal generatedby the road grade sensor and shown as a force.

, one or more vehicle wheel brakes schematically illustrated as brake12. A source of brake pressure, such as master cylinder 14, is connectedthrough the wheel brake pressure modulator .16 to the wheel cylinder ofthe brake 12. Brake 12 may be a front wheel brake, a rear wheel brake,or any desirable combination thereof. The modulator 16 is controlled byvalves 18 and 20, which are electrically actuated and are, in turn,respectively controlled by switches 22 and 24. Other than providing anoperative structure, the modulator 16, with its valves 18 and 20, fonnno part of the invention. The modulator may be hydraulically orpneumatically operated under the control of valves 18 and 20. Systemshaving modulators which may be utilized in practicing the invention aredisclosed and claimed in U.S. Pat. No. 3,592,5l4, issued July 13, 1971,to Del lofi; and U.S. Pat. application Ser. No. 128,484, filed Mar. 26,1971, which is a continuation of U.S. Pat. application Ser. No. 806,807,filed Mar. 13, 1969 by Van Ostrom et al., now abandoned.

The control system components include the road grade sensor 26, thebrake torque sensor 28, the vehicle speed simulator 30, the wheel speedsensor 32, the vehicle speed simulator modifier 34, the forceaccumulator link 36, the switch cam 38, the force balance adjuster 40,and the percent slip modifier 42. Some of these components arecircumfercntially arranged about the axis of link 36, with only theupper portion being shown for simplicity. I

The force accumulator link 36 is rotatable and slidably mounted in thebearing and guide 44, has a disc 46 on one end, a bearing retainer 48 onthe other end, and mounts the inner race of the thrust bearing 50. Theinner race of this bearing abuts retainer 48 and the outer race isprovided with a wear ring 52. The end of force accumulator link 36adjacent bearing retainer 48 forms a part of thrust bearing 50,schematically illustrated as including the center ball 54. Ball 54engages the end of the switch cam 38 so that linear force is transmittedbetween link 36 and cam 38, but not rotational force.

The frame 56 anchors the main support bearings 58 and 60 which supportthe wheel speed sensor 32. Sensor 32 includes a flyweight arrangement toproduce a force signal proportional to wheel speed. The sensor includesthe annular drive and inertia ring 62, to which are pivotably mountedflyweights 64. Only one such flyweight is shown. The flyweight includesa bellcranklike arrangement with the arm 66 having its end engaging thewear ring 52. As the flyweight 64 moves radially outward, it urges theforce accumulator link 36 to the right through arm 66 and thrust bearing50. A one-way clutch and bearing arrangement 68 is provided on the innerperiphery of ring 62, and includes inertia ring 70. This ring mountsbearing and guide 44. The outer periphery of ring 62 is formed as apulley and receives drive belt 72. This belt is suitably driven by thewheel associated with wheel brake 12; this construction beingschematically illustrated. In practice, other driving arrangements maybe made. Also, in some instances, the drive may be from the vehicledrive shaft which drives both rear wheels through the differential. Asused herein, the term wheel speed sensing is considered to besufficiently broad to include sensing rotational speed through suchdrive arrangements. Therefore, signals generated in accordance with orrelated to wheel speed are considered to include such variations.

Ring 70 is also a part of the vehicle speed simulator 30 and hasflyweights pivotably secured thereto, one such flyweight 74 beingillustrated. This flyweight is similar in construction to flyweight 64and includes a bellcrank arm 76, which has its outer end engaging thedisc 46 so that radially outward move ment of fiyweight 74 causes aleftward force to be exerted on force accumulator link 36 through arm 76and disc 46.

The one-way clutch and bearing unit 68 provides the means fortransmitting wheel-accelerating motion to the vehicle speed simulatorand then allows the vehicle speed inertia ring 70 freedom to overrun thewheel speed sensor ring 62 when the wheel decelerates. A thrust bearing78 between a part of ring 70 and a part of ring 62 supports the reactionforce to the vehicle speed simulator signal. The vehicle speed simulatoroperates to produce a force signal proportional to simulated vehiclespeed.

The overrunning action of inertia ring 70 will simulate vehicle speed sothat the simulated speed is approximately the same as actual vehiclespeed when the wheel is decelerated The vehicle speed simulator modifier34 includes an annular brake disc 80 which is provided with a suitablefriction braking material 82, an annular friction plate 84 which isguided in axial movement by guide pins 86, and plate-actuating means 88.The actuating means includes a housing having cylinders 90 and 92 formedtherein and in which piston 94 and 96 are respectively mounted forreciprocation. The pistons are connected to plate 84 so that, as theyare urged to the right by pressure in their respective cylinder, theyincrease the engaging force acting on the plate against brake lining 82.As the force acting on plate 84 increases, the inertia ring 70 is causedto decelerate in proportion to vehicle deceleration caused by braketorque and the road grade over which the vehicle is operating.

In order to accomplish this, the brake torque sensor is connected sothat its torque-sensing input arm 98 acts through its piston 100 topressurize hydraulic fluid in its cylinder 102. Cylinder 102 is fluidconnected to cylinder 90 in a closed circuit so that an increase inpressure occurs in cylinder 90 in accordance with an increase inpressure in cylinder 102. Cylinder 102 is also fluid connected to thepercent slip modifier 42 as will be described.

The road grade sensor 26 acts to generate a pressure in its cylinder104, which is fluid connected to cylinder 92 through a closed circuit sothat the pressure in cylinder 92 is in proportion to the pressuregenerated in cylinder 104. The piston 106 of road grade sensor 26,acting in cylinder 104, is schematically illustrated as being moved byarcuate movement of arm 108 about the axis 110 of the road speed sensoroutput gear 112. The road speed sensor 26 also includes gears 114 and116, respectively mounted for rotation about their axes 118, 120. Gears114 and 1 16 are meshed with each other, and gear 116 is meshed withgear 112. Thus, gear 112 follows arcuate movement of the other twogears, and those other two gears are connected to act together. The gearaxes 110, 118 and 120 are parallel to each other and extend transverselyof the vehicle in which the system is installed. This is indicated bythe diagrammatic showing of the forward direction and upward directionof the vehicle. Gear 114 has a weight 122 secured to it, and gear 116has a similar weight 124 secured to it. These weights are movable withtheir respective gears about axes 1 l8 and 120 in a vertical planeperpendicular to the gear axes and parallel to the vehicle center line.The weights have like vertical components of extension; that is, theyboth have a downward component extension, as illustrated, or may bothhave an upward component of extension; and they further extend withopposite outward components of extension. Thus, weight 122 has arearward component of extension in relation to the vehicle and weight124 has a forward component of extension in relation to the vehicle. Itis preferable to attach the road speed sensor unit to the vehicle axleto eliminate the effects of body deflection allowed by the vehicleduring deceleration. The sensor creates an hydraulic pressure signal incylinder 92, in accordance with the grade of the road on which thevehicle is moving. This pressure generates a force signal transmittedthrough piston 96 to plate 84. This force signal modifies the simulatedvehicle speed signal to compensate for the effect of road grade onvehicle deceleration. The road grade sensor weights 122 and 124 act withequal and opposite torques on their respective gears 1 14 and 116,resulting from the force of gravity on the weights. This results in aposition of equilibrium in which there is no net torque output from theweights so long as there is no change in road grade. Vehicleacceleration and deceleration will not change the weight equilibriumposition since the weights experience equal and opposite inertia forcesin response to vehicle acceleration and deceleration. Therefore, thegears 114 and'116 are maintained in the unchanged equilibrium position.

When the road grade changes to an upward grade, the torque output ofweight 124 increases while the torque output from weight 122 decreasesbecause of the change in effective torque arm length, assuming thevehicle to be traveling in a forward direction up the grade. Thisresults in a torque imbalance transmitted through gear 116 to outputgear 112, arm 108, and piston 106 to increase the hydraulic pressure incylinders 104 and 82. When the vehicle is being driven forwardly andencounters a descending road grade, the reverse situation occurs and theresulting torque imbalance is transmitted to cause a decrease inpressure in cylinders 104 and 92. Thus, the amount of force generated bypressure in cylinder 92, and acting on plate 84, varies in accordancewith the road grade. The road grade signal causes an increase in brakingforce on lining 82 when an ascending grade is encountered, therebymodifying the simulated vehicle speed signal to account for the fastervehicle speed deceleration under such circumstances.

The percent slip modifier 42 includes a housing 126 with a chamber 128and a power wall 130, sealing one end of the chamber. The chamber isfluid connected to the closed hydraulic system of the brake torquesensor 28 through conduit 132. Therefore, the pressure signal indicatingbrake torque, generated in cylinder 102, is delivered to move the powerwall 130. A push rod 134 is connected to be moved by power wall and hasits outer end engaging the end of force accumulator link 36 on whichdisc 46 is provided. Thus, the percent slip modifier utilizes the braketorque signal to modify the summation of the simulated and modifiedvehicle speed signal and the wheel speed signal as they are applied tothe force accumulator link.

The force balance adjuster 40 includes a compression spring 136 engagingthe end of switch cam 38 opposite torque bearing 54 and a springcompression force adjuster, illustrated as adjusting screw 138. Thecompression force of spring 136 is adjusted to balance the forceaccumulator link so as to properly index the switch cam.

The switch cam includes a pair of lands 140 and 142 separated by abeveled groove 144. Switch 22 has a cam follower 146 and switch 24 has acam follower 148. These followers are in engagement with the cam 38 andride on either land 140 or land 142 or in groove 144. As is moreparticularly shown in FIG. 3, when the system is in the brake pressureapply condition, both switches 22 and 24 are held open since their camfollowers 146 and 148 are both in engagement with cam land 140.

When the command signal generated by the system is such that the forceaccumulator link moves leftwardly to require a brake pressure releaseposition, it moves through the brake pressure slow apply position ofFIG. 5. In the brake release position, cam follower 146 is in groove 144so that switch 22 is closed. Cam follower 148 engages land 142 so thatswitch 24 is open. In this condition, valve 18 will be open while valve20 will be closed, controlling the modulator 16 to release wheel brakeapply pressure delivered to the brake 12. When the force accumulatorlink 36 moves cam 38 rightwardly from the brake pressure releaseposition, it establishes the brake pressure slow apply position of FIG.4 in which switch 22 is open and switch 24 is closed. This causes themodulator 16 to slowly apply the brake apply pressure. Further rightwardmovement of the force accumulator link 36 and of cam 38 returns thesystem to the brake pressure apply position shown in FIG. 3. In thisposition, pressure from the master cylinder 14 is delivered to the brake12.

The graphs of FIGS. 6 through 10 relate the output signal to thegenerating parameter. The curves are provided as examples, and curvesfor any particular hardware may vary somewhat, but will follow thegeneral pattern set forth. The output signals are illustrated as forcesplotted against speed in FIG. 6. Curve 150 indicates the force signalobtained from the vehicle wheel speed sensor 32. Curve 152 indicates theforce signal generated by the vehicle speed simulator 30. Curve 154 ofFIG. 7 indicates the force signal generated by the brake torque sensor28. Curve 156 of FIG. 8 plots flyweight torque developed and thusincrease the force signal generated by the brake torque sensor. Thisincreases signal acting on the vehicle speed simulator 30 through themodifier 34 will ofiset the decreases force signal accomplished by thedecrease in deceleration against the force signals acting through thevehi- 5 wheel speed as sensed by wheel speed sensor 32. This will conclespeed simulator modifier 34. Curve 158 of FIG. 9 plots the tinue untilthe wheel-to-road torque cannot be increased. This force signal of theroad grade sensor through a range of road point occurs at the high pointof the appropriate curve of FIG. grades from a 27 percent descendinggrade to a 27 percent 10. Beyond this point, the vehicle wheel will havea large ascending grade. Curves 160, 162, 164 and 166 plot brakedeceleration and brake torque will also decrease. The force torqueagainst the percent slip of the wheel to the road surface 10 balancewill shift, causing the force accumulator link 36 to be with fourdifferent road surface conditions. These conditions moved furtherleftwardly by the command signal until the relate to a dry concretesurface; a wet road surface; a road surswitch cam 38 is in the brakerelease position of FIG. 5. This face covered with snow, and anice-covered road surface. will further reduce the brake torque and willallow the vehicle These four curves have been well established in theprior art. wheel to accelerate. When the wheel speed has increased suf-The operational sequence occurring in the system will now ficiently todevelop a substantially large force signal by means be described. In thenormal condition of operation of the vehiof the wheel speed sensor toagain change the command cle brake system, the cam 38 is in the positionshown in FIG. 3 signal, the force accumulator link 36 and the cam 38will be and the vehicle brakes operate without being affected by themoved to the right, and cam 38 will assume either the slow controlsystem. When the vehicle is driven on a road at a apply or the fullapply position depending on the magnitude of steady speed, the vehiclespeed inertia ring 70 and the wheel the signal, which, in turn, dependson the magnitude of the speed inertia ring 62 will be driven at the samespeed. The speed difi'crcnceswheel speed ring 62 drives the vehiclespeed ring 70 through Control of the deceleration of the inertia ring70, utilized to the one-way clutch 68. The force signals generated bythe e simulate vehicle speed, is regulated by the amount of force extwosensors are equal and, therefore, the force exerted in operted throughthe modifier 34. In addition to the brake torque posite directions onforce accumulator link 36 are equal and force sign the r grade Sensor 26g n ates another force opposite. In this force balance condition, withthe brakes signal acting through piston 96 and brake plate 84. Bycombeing released, spring 136 holds the force accumulator link 36 biningb ake torque signals and road grade signals, the vehicle and the cam 38in the brake apply position illustrated in FIG. sp e Simulalo! ng 7 iecel r te! to provide a good ap- 3. When the vehicle brakes are applied,the vehicle wheel, to 30 p i n of actual vehicle p rm r the p r whichwheel speed sensor is operationally connected by belt ip m ifi r a ts ina cordance with changes in brake torque 72, decelerates. This causes adeceleration of ring 62 and to modify the summation of signals from thewheel speed senflyweights 64. However, by action of the one-way clutch68, scr 32 n h vehicle speed simulator as modified hr gh the vehiclespeed simulator ring 70 overruns due to its inertia. modlfiel' tofurther fin the mman ignal. The control force balance therefore changeswith this dif- 35 The 8 chm Information Provides a ready ferential inspeed between the two speed sensor units, tendi panson of conditions ofvarious elements of the system under to move the force accumulator link36 leftwardly. In addition, each of Operation- Master cylinderpressurized Master cylinder Brakes applied- Brakes applied- Unit orSignal released normal wheel slipping Brakes released Vehicle wheelsgeed(Si) teady state Decelerate Decelerate Accelerate Degglgmtg. Vehiclespeed i) ..do do do Decelelating. D0, Vehicle speed control force si nal(F,) Sl=Sg Si=Sr S1 S S1 S, S1 S2 voli irale wheel speed control orcesignal Fl Fg FI F1 Fi Fi Fi F Fl Fa l Wheel brake torque control forcesignal 0 Increasing Stgady toi Decressing. Decreasing.

BOIBBS D Com mand signal-summation of control 0 g force signals (Fi i+a)- Vehicle speed simulator flywheel brak- Zero Zero or decreasing- Veryslowly Decreasing.-. Decreasing.

il'lg torque. increasing. Response rate Fast-- Fast Gradually Fast Fast,switch cam position" To right To right Center To lclt To left. Switchcondition:

Switch 24.- Open pen Closed Switch 22.. 0 ..do Modulator hydraulicsection Open to master Open to master cylinder. cylinder or inincreasingpressure. Brake apply pressure None creasing Gradually DecreasinDecreasing.

increasing. Brake torque d0 J10 ..do do Do.

1 Closed to master olyinder and increasing pressure or moving towardreopening to master cylinder pressure. 3 Closed to master cylinder anddecreasing pressure or moving toward vs the brake torque sensor 28generates a brake torque signal acting through piston 94 and the vehiclespeed simulator modifier 34 to decelerate the ring 70 in accordance withbrake torque causing another force signal change.

The comparison of these force signals results in a command signalgenerated as a force signal transmitted from the force accumulator linkto switch cam 38, and spring 136 moves the switch cam leftwardly. Whenthe percent slip, or wheel speed separation from vehicle speed, issufficiently large, cam 38 will be located in the brake pressure slowapply position shown in FIG. 4. The slow apply brake pressure will allowa gradual inve closing.

While in the abovedescription reference is generally made to sensingspeeds, it is also within the scope of the invention to sensedecelerations and accelerations and to utilize signals of this nature.Such signals are therefore also referred to as movement characteristicsignals. The invention is disclosed as a mechanical-hydraulic system,but may also be practiced by use of other types of sensing and signalaccumulating or combining devices. The elements of the control systemmay be electrical, pneumatic or hydraulic, or a combination thereof. Thetype of vehicle braking system in which the invention is utilized may beother than the hydraulic system schematically crease in brake efiortwhich will also increase the brake illustrated, such as positive airpressure, electrical, or elec tromagnetic in nature. It is only in itsmove specific aspects, as more particularly disclosed and claimedherein, that the invention applies to a mechanical system andparticularly to a mechanical road grade sensor.

What is claimed is:

I. In combination in a vehicle wheel slip control system for controllingthe brakes of one or more vehicle wheels, the combination of:

means sensing wheel speed of the wheel brake to be controlled andgenerating a wheel speed signal,

means selectively driven in accordance with wheel speed simulating speedof the vehicle being braked approximating actual vehicle speed duringbraking and generating a simulated vehicle speed signal,

means sensing the road grade of the road on which the vehicle is movinga generating a road grade signal,

signal modifying and comparing and generating means receiving said roadgrade signal and modifying at least one of said speed signals inaccordance with said road grade signal and comparing said speed signalsas modified and generating therefrom a wheel brake pressure commandsignal,

and means including a wheel brake pressure modulator receiving saidcommand signal and controlling wheel brake pressure in response to saidcommand signal to control wheel slip.

2. The combination set forth in claim 1 further comprising:

means sensing the brake torque generated by the wheel brake beingcontrolled and generating a wheel brake torque signal,

said signal modifying and comparing and generating means also receivingsaid torque signal and modifying at least one of said speed signals inaccordance with said torque signal.

3. The combination set forth in claim 1 further comprising:

means sensing the brake torque generated by the wheel brake beingcontrolled and generating a wheel brake torque signal,

and means receiving said brake torque signal and modifying said wheelbrake pressure command signal in accordance with wheel-to-road slip as afunction of sensed brake torque.

4. In the combination set forth in claim 1,

said means driven in accordance with wheel speed being connected indriven relation with said wheel speed sensing means.

5. In the combination set forth in claim 1,

said simulated vehicle speed signal being modified by said road gradesignal.

6. In the combination set forth in claim 1,

said speed and command signals being forces with said command signalbeing the summation of said compared speed signals and acting linearlyin either of two opposite directions and including the force node as acenter,

switch-actuating means responsive to said command signal,

and switches actuated by said switch-actuating means for controlling theopening and closing of valves of said modulator to apply and releasewheel brake pressure to the extent required to control wheel slip.

7. The method of controlling vehicle wheel slip comprising the steps of:

a. sensing a wheel rotational characteristic and generating a wheelmovement characteristic signal, b. simulating a vehicle linear movingcharacteristic and generating a simulated vehicle movementcharacteristic signal,

c. sensing the road grade on which the vehicle is moving and generatinga road grade signal,

d. modifying one of said characteristic signals by the road gradesignal,

e. combining the modified movement characteristic signal and the othermovement characteristic signal and generating a wheel brake applypressure command signal,

f. and selectively changing wheel brake apply pressure in accordancewith the command signal to selectively apply wheel brake pressure to awheel brake for the sensed wheel and to release wheel brake pressureapplied to the wheel brake for the sensed wheel.

8. The method of claim 7 in which in step (b) the simulated vehiclemovement characteristic signal is generated with a wheel brake torquesignal as a component thereof, and in step (d) the simulated vehiclemovement characteristic signal is modified by the road grade signal.

9. The method of claim 7, in which in step (f) includes selectivelychanging wheel brake apply pressure from a full apply to anothercondition which may be a slow apply or a pressure release as required bythe command signal to control wheel slip, and reapplying wheel brakeapply pressure as permitted by the command signal.

t t t t 5 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PatentNo- 3,632,176 Dated January 4, 1972 Invencort's) Edward G. Gaeke It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below: I

Column 1, line 28, delete entire line and first two words "1 in line 29,as follows: "may be braked more quickly, while vehicles descending alarge grade.

Column 3, line 24, after the word "sensor" insert 28 Column 4, line 54,after "FIG." delete "5" and insert 4 to the brake pressure releaseposition of FIG. 5 Column 5-6, in the Chart: In the line for Commandsignal,

the dashes should also appear in the last column, In the line for theSwitch condition of Switch 22, "do do do do Closed. Should read do doOpen Closed Closed Column 6, line 2, the word "increases" should readincreased Column 6, line 4, the word "decreases" should read decreased 7Column 7, line 1, the word "move" should read more Column 7, Claim 1,line 16, the word "a" (first occurrence) should read and Signed andsealed this 27th, day. of June 1972.

(SEAL) Attest:

EDWARD MJLETCHER, JR; ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents

1. In combination in a vehicle wheel slip control system for controllingthe brakes of one or more vehicle wheels, the combination of: meanssensing wheel speed of the wheel brake to be controlled and generating awheel speed signal, means selectively driven in accordance with wheelspeed simulating speed of the vehicle being braked approximating actualvehicle speed during braking and generating a simulated vehicle speedsignal, means sensing the road grade of the road on which the vehicle ismoving and generating a road grade signal, signal modifying andcomparing and generating means receiving said road grade signal andmodifying at least one of said speed signals in accordance with saidroad grade signal and comparing said speed signals as modified andgenerating therefrom a wheel brake pressure command signal, and meansincluding a wheel brake pressure modulator receiving said command signaland controlling wheel brake pressure in response to said command signalto control wheel slip.
 2. The combination set forth in claim 1 furthercomprising: means sensing the brake torque generated by the wheel brakebeing controlled and generating a wheel brake torque signal, said signalmodifying and comparing and generating means also receiving said torquesignal and modifying at least one of said speed signals in accordancewith said torque signal.
 3. The combination set forth in claim 1 furthercomprising: means sensing the brake torque generated by the wheel brakebeing controlled and generating a wheel brake torque signal, and meansreceiving said brake torque signal and modifying said wheel brakepressure command signal in accordance with wheel-to-road slip as afunction of sensed brake torque.
 4. In the combination set forth inclaim 1, said means driven in accordance with wheel speed beingconnected in driven relation with said wheel speed sensing means.
 5. Inthe combination set forth in claim 1, said simulated vehicle speedsignal being modified by said road grade signal.
 6. In the combinationset forth in claim 1, said speed and command signals being forces withsaid command signal being the summation of said compared speed signalsand acting linearly in either of two opposite directions and includingthe force node as a center, switch-actuating means responsive to saidcommand signal, and switches actuated by said switch-actuating means forcontrolling the opening and closing of valves of said modulator to applyand release wheel brake pressure to the extent required to control wheelslip.
 7. The method of controlling vehicle wheel slip comprising thesteps of: a. sensing a wheel rotational characteristic and generating awheel movement characteristic signal, b. simulating a vehicle linearmoving characteristic and generating a simulated vehicle movementcharacteristic signal, c. sensing the road grade on which the vehicle ismoving and generating a road grade signal, d. modifying one of saidcharacteristic signals by the road grade signal, e. combining themodified movement characteristic signal and the other movementcharacteristic signal and generating a wheel brake apply pressurecommand signal, f. and selectively changing wheel brake apply pressurein accordance with the command signal to selectively apply wheel brakepressure to a wheel brake for the sensed wheel and to release wheelbrake pressure applied to the wheel brake for the sensed wheel.
 8. Themethod of claim 7 in which in step (b) the simulated vehicle movementcharacteristic signal is generated with a wheel brake torque signal as acomponent thereof, and in step (d) the simulated vehicle Movementcharacteristic signal is modified by the road grade signal.
 9. Themethod of claim 7, in which in step (f) includes selectively changingwheel brake apply pressure from a full apply to another condition whichmay be a slow apply or a pressure release as required by the commandsignal to control wheel slip, and reapplying wheel brake apply pressureas permitted by the command signal.